Direct Depth- and Lateral- Imaging of Nanoscale Magnets Generated by Ion Impact.

Falk Röder,Jürgen Fassbender,Sebastian Wintz,Jürgen Lindner,René Hübner,Lothar Bischoff,Gregor Hlawacek,Hannes Lichte,Kay Potzger,Rantej Bali

doi:10.1038/srep16786

Falk Röder, Jürgen Fassbender + Show 8 more

Open Access

https://doi.org/10.1038/srep16786

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Abstract

Nanomagnets form the building blocks for a variety of spin-transport, spin-wave and data storage devices. In this work we generated nanoscale magnets by exploiting the phenomenon of disorder-induced ferromagnetism; disorder was induced locally on a chemically ordered, initially non-ferromagnetic, Fe60Al40 precursor film using nm diameter beam of Ne+ ions at 25 keV energy. The beam of energetic ions randomized the atomic arrangement locally, leading to the formation of ferromagnetism in the ion-affected regime. The interaction of a penetrating ion with host atoms is known to be spatially inhomogeneous, raising questions on the magnetic homogeneity of nanostructures caused by ion-induced collision cascades. Direct holographic observations of the flux-lines emergent from the disorder-induced magnetic nanostructures were made in order to measure the depth- and lateral- magnetization variation at ferromagnetic/non-ferromagnetic interfaces. Our results suggest that high-resolution nanomagnets of practically any desired 2-dimensional geometry can be directly written onto selected alloy thin films using a nano-focussed ion-beam stylus, thus enabling the rapid prototyping and testing of novel magnetization configurations for their magneto-coupling and spin-wave properties.

Highlights

Ion-irradiation can modify a variety of magnetic properties in alloys, including the magnetization easy axes, magnetic anisotropy, coercive fields and ferromagnetic resonances[10,11]
We focus on ion-induced magnetization due to chemical disordering, taking Fe60Al40 thin films as our model system
Alloys possessing disorder-induced ferromagnetism phenomena usually consist of atoms of magnetic and non-magnetic species, and magnetic phase transitions can be triggered by chemical disordering

Summary

Introduction

Ion-irradiation can modify a variety of magnetic properties in alloys, including the magnetization easy axes, magnetic anisotropy, coercive fields and ferromagnetic resonances[10,11]. We focus on ion-induced magnetization due to chemical disordering, taking Fe60Al40 thin films as our model system This is a powerful way to directly write magnetic nanostructures using ions, as it is a physical process that involves the displacement of only a few atoms within the lattice to generate large magnetization, while preserving the flat topography of the original film. For high resolution work the beam tails are reduced to a minimum by using a small aperture and placing the beam crossover at a large distance from the aperture This ion-optics design ensures that ions originating from a single ionization site only (i.e., only one of the three apex atoms) can reach the sample, resulting in a narrow beam of ∼2 nm diameter in case of Ne+ ions. Estimations of the homogeneity and sharpness of ion-induced magnetic patterns have been achieved via direct observations

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